Field of the Invention
The invention relates to the field of biomass energy, and more particularly to a method and system for cogenerating gas-steam based on gasification and methanation of biomass such as rice husk, straw, and sawdust.
Description of the Related Art
Crude syngas generated from biomass gasification contains a lot of CO, H2, CO2, etc., and is not suitable for direct use as a city gas and a fuel for combined cycle power plant because of its low calorific value and CO toxicity. Natural gas is suitable for use as a city gas and a fuel for combined cycle power plant because of its high calorific value and non-toxicity. In the presence of a catalyst, CO and CO2 can be completely converted to methane, which is the synthetic substitute natural gas (SNG). Main reaction of the methanation is as follows:CO+3H2→CH4+H2O ΔH0θ=−206 kJ/mol.
Conventional method and system for producing gas-steam employ non-renewable coal as the raw material. The methanation reaction uses a molybdenum sulfide catalyst, the syngas conversion efficiency is low, and the processing capacity is limited. In addition, the isothermal reactor has complex design, complex structure, and high manufacturing costs, difficult mechanical amplification, so it is difficult for loading and unloading of catalysts. The methods impose harsh requirements for catalysts, the heat exchange efficiency between the product gas and steam circulation system is low, and the high quality steam and the reaction heat cannot be recycled, thereby leading to low recovery efficiency of methanation reaction heat.